Mobile Internet Protocols (IP) provide a procedure for communicating using Internet Protocol (IP) packets to support IP based communications in mobile communications networks. One feature of Mobile IP is to provide a scheme in which a mobile node may move from one network to another whilst ensuring that IP packets addressed to the mobile node can be sent to that mobile node using the same IP address as used to deliver IP packets and receive IP packets when the mobile node was connected to its home network.
One feature of Mobile IP is the mechanism by which a mobile node moves between networks. This is achieved by associating a mobile node with a home network and a home agent. IP packets which are to be sent to the mobile node are addressed to the mobile node's home address, within the mobile node's home network. The home agent monitors incoming packets to the home network and intercepts packets sent to the mobile node's home address if the mobile node has moved to another network. The home agent then forwards any intercepted packets to the mobile node, via the mobile access network to which the mobile node is currently attached.
For this arrangement to work the home agent has to be informed of the mobile node's whereabouts. When the mobile node detects it has moved from its home network to a visited network, it negotiates a care of address. The care of address is a temporary address allocated to the mobile node by the visited network. The mobile node then sends a binding update request to the home agent. The binding update request includes the temporary care of address. When the home agent receives the binding update request from the mobile node it performs a binding update procedure which enables IP packets to be sent to and from the mobile node. The binding update procedure differs depending on what version of the IP standard is being used (i.e. IPv4 or IPv6), but typically may involve establishing tunneling between the home agent and the mobile node. Other functions may also be performed before, during or after the binding update such as subscriber identification, authorisation and billing. It is an aim of the mobility support in Mobile IP, that movement between networks is transparent to a user. Therefore a mobile node engaged in a data communications session such as a voice call or an internet session, ideally should not experience a noticeable interruption or delay in data transmission.
In some scenarios, “hotspots” in airports or moving transport systems such as trains for example, there might be a high number of mobile nodes moving between networks. As a result, a correspondingly high number of binding update requests and high demand on parts of the network performing binding update procedures may result. If demand is sufficiently high, delays and interruptions in data transmissions may result. These delays may be noticeable to users engaged in applications requiring real time, or near real time data transmission such as voice calls or instant messaging.